Top Alternatives to Nagios

Port Monitor is an easy tool that does website and server monitoring 24/7 every 60 seconds for free.

Zabbix is enterprise open source monitoring software for networks and applications.

AppBeat is reliable website monitoring service that alerts you when there is a downtime or failure. It also measures performance and provides functional tests.

Spiceworks is a professional network for the information technology (IT) industry.

Datadog is a monitoring service for cloud-scale applications, bringing together data from servers, databases, tools, and services to present a unified view of an entire stack.

NetCrunch is a Windows Server–based network monitoring tool that boasts high performance and impressive scalability even in a single-server deployment.

Munin is a networked resource monitoring tool that can help analyze resource trends.

Dynatrace APM tools provide user experience analysis that identifies and resolves application performance issues faster than ever before.

Total Network Inventory is a PC audit and software inventory management solution.

Pandora FMS (Pandora Flexible Monitoring System) is software for monitoring computer networks.

Domotz Pro Remote Network Monitoring Software and Network Management System.

PRTG is a network monitoring tool that helps you to ensure that your computer systems are running smoothly and that no outages occur.

HappyApps is an online app uptime monitoring platform.

Icinga is an open source computer system and network monitoring application.

CoScale delivers full stack performance monitoring, optimized for large production and container environments, and powered by anomaly detection.

Observium is a low-maintenance auto-discovering network monitoring platform supporting a wide range of device types, platforms and operating systems, etc.

Monitis is a web performance monitoring platform.

Mindarray is a network monitoring software which includes BSM, SLA with real time monitoring & analytics.

Cacti is a network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality.

LibreNMS is an auto-discovering PHP/MySQL-based network monitoring system.

Pulseway is a mobile-first IT management software.

The Dude network monitor automatically scans all devices within specified subnets, draw and layout a map of your networks, monitor services of your devices and alert you in case some service has problems.

Lansweeper Network Inventory is an agentless IT asset management and Network Inventory software tool for Microsoft Windows.

IT Asset Tool is a free software to inventor and monitor your network.

Monit is a free, open source process supervision tool for Unix and Linux.

PHP Server Monitor is an open source tool to monitor your servers and websites.